1. Field of the Invention
This invention relates to a high density miniature sensor circuit on a ceramic substrate. The circuit is used in combination with a wiper blade that passes over contact pads of the circuit and converts the position of the wiper arm to predetermined electrical resistance values. The sensor circuit can be used to record liquid pressures in a closed chamber, for example, to record the oil pressure in an automobile motor crankcase.
2. Prior Art
Existing circuits convert the position of a wiper arm to a predetermined resistance value by spacing the contact pads therein as close together as thick film technology allows. This is about 0.010 inches. Also the width of the contact pads is the minimum width that thick film technology permits. This is also about 0.010 inches. This is done to provide a maximum number of steps during movement of the wiper arm. In order to print and trim individual resistors between each contact pad, greater area is needed. This greater area is found by fanning the contact pads out away from the area where the wiper arm travels and putting the resistors in this larger area (at the far end of the contact pads). In accomplishing this, the conductors (contact pads) in the circuit are made long relative to the size of the substrate. The resistance in the conductor itself becomes significant and can exceed the allowable resistance change at a given step.
It is an object of this invention to provide a thick film conductor and resistor circuit capable of converting wiper arm position to a predetermined resistance value, which circuit has very small resistance changes pwer step. The conductors in the circuit also act as contact pads for the wiper arm blade.
Another object of this invention is to provide a thick film conductor and resistor circit that will withstand many cycles of wiper arm movement without wearing out.
Still another object of this invention is to provide a method for making the circuit so that there are very small distances between steps thereon, enabling the circuit to be placed on a very small area substrate.